Magnetic brush developing apparatus for copiers

ABSTRACT

An electrostatic type copier or reproduction machine having one or more magnetic brush devices for developing the latent electrostatic images formed on the copier photoconductive member, such magnetic brush devices ordinarily having a biasing voltage impressed thereon. To enable shorting of the magnetic brush or brushes to be detected, and, where desired, the shorted brush of a multiple brush system to be identified, a short responsive circuit is provided adapted when shorting is detected to actuate a predetermined control. The aforesaid control may comprise an operator signal lamp or a device to shutdown the copier.

United States Patent [1 1 Wilson Feb. 18, 1975 1 MAGNETIC BRUSHDEVELOPING APPARATUS FOR COPIERS [75] Inventor: Charles D. Wilson,Fairport, NY.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

22 Filed: Apr. 25, 1973 21 Appl. No.: 354,416

[52] U.S. Cl 118/10, 1l7/17.5, 118/11, 118/637,118/4 [51] Int. Cl G03g13/00 [58] Field of Search 118/7, 9, 10, 11,637; 117/175 [56] ReferencesCited UNITED STATES PATENTS 2,902,974 9/1959 Greaves 118/637 3,219,01411/1965 Mott et al. 118/637 3,638,614 2/1972 Young et al. 118/6373.674.532 7/1972 Morse; 118/637 x 3,779,204 12/1973 Altmann 118/83,795,239

3/1974 Walberg", 317/3 Primary Examiner-Mervin Stein AssistantE.\'aminerLeo Millstein [57] ABSTRACT 7 Claims, 7 Drawing FiguresFATENTED FEB18I875 SHEET 1 BF 4 FATENTEU FEB l 8|975 SHEET P. 0F 4PATENTED FEB] 8l975 3.666564 sum nor 4 MAGNETIC BRUSH DEVELOPINGAPPARATUS FOR COPIERS This invention relates to a magnetic brushdeveloping system for reproduction machines, and more particularly, toan improved magnetic brush developing system having means for detectingshorting of the system magnetic brush or brushes.

As will be understood by those familiar with electrostatic typereproduction and copier machines, the efficacy of such copiers dependsin large measure upon the proper relative charge, i.e. the electrostaticdevelopment field, being maintained between the copier photoconductivemember and the image developing materia. For, as appreciated, thiselectrostatic development field is relied upon to attract the inkportion of the developing material, i.e. the toner, to thephotoconductive member in conformance with both the outline and densityof the electrostatic latent image on the photoconductive member. It willbe understood that the electrostatic image was previously formed throughexposure of the charged photoconductive member to a light image of theoriginal being copied.

Many copiers employ one or more magnetic brushes to bring the developingmaterial into operative relationship with the photoconductive member. Ineffectuating this, the magnetic field generated by the brush or brushesserves initially to attract and hold the developing material on theperiphery thereof and thereafter, due to the charge relationship betweenbrush and photoconductive member, to release toner attracted to thephotoconductive member in conformance with the latent electrostaticimage. In this context, the developing material is composed of carrierparticles or beads and toner, the toner particles, due to thetriboelectric relationship between the carrier and toner materials,being normally attracted to the carrier. It is this carrier bearingtoner that is brought by the developing mechanism, i.e. the aforesaidmagnetic brushes, into juxtaposition with the photoconductive member toallow the electrostatic charges on the photoconductive member to drawthe toner from the carrier beads and onto the photoconductive member inconformance with the latent electrostatic image thereon.

While the aforesaid carrier may comprise various materials and materialcompositions, in the case of magnetic developing systems, the carriermaterial must have magnetic properties in order for the magnetic brushor brushes to operate. However, this may give rise to a shorting problemsince the magnetic carrier beads, which are normally a ferrite material,can, should they jam or conglomerate between a magnetic brush and thedeveloping material housing, which is normally grounded, short thebrush. This condition, which alters the operating bias on the magneticbrush or brushes affected, impairs or destroys developing efficacy.

It is a principal object of the present invention to provide a new andimproved magnetic developing system for electrostatic type reproductionmachines.

It is an object of the present invention to provide an electrostaticcopier with magnetic brush type developer incorporating means to detectfaulty operation of the magnetic brushes.

It is a further object of the present invention to provide a magneticbrush type developing apparatus for reproduction machines having meansto signal the presence of ashort circuit in the magnetic brushdeveloping apparatus.

It is an object of the present invention to provide an improvedelectrostatic copier having a multiple magnetic brush developer systemincorporating means to identify a shorted brush.

It is another object of the present invention to provide an improvedreproduction machine with magnetic brush developer having meansresponsive to a short in the developer to shut down the reproductionmachine.

This invention relates to a reproduction machine for producing copies oforiginals, comprising, in combination, a photoconductive member adaptedto be electrostatically charged to permit latent electrostatic images ofan original being reproduced to be formed thereon during thereproduction process; developer means to bring developer material intooperative relationship with the photoconductive member to develop thelatent electrostatic image on the photoconductive member in preparationfor transfer thereof to a supportmaterial, the developer means includingat least one magnetic brush; means to provide a biasing voltage to themagnetic brush; and means adapted on shorting of the magnetic brush togenerate a predetermined signal.

Other objects and advantages of the present invention will be apparentfrom the ensuing description and drawings in which:

FIG. 1 is a schematic sectional view of an electrostatic typereproduction machine incorporating the magnetic brush developingapparatus of the present invention;

FIG. 2 is a side view of the magnetic brush developing apparatus shownin FIG. 1;

FIG. 3 is an elevational view of the opposite side of the magnetic brushdeveloping apparatus shown in FIG. 2 illustrating'the brush drives;

FIG. 4 is a top plan view of the magnetic brush developing apparatusshowing details of the brush biasing means;

FIG. 5 is a first circuit embodiment illustrating the magnetic brushshort detecting circuit of the present invention;

FIG. 6 is a second circuit embodiment illustrating a magnetic brushshort detecting circuit effective to pinpoint the specific brushshorted; and

FIG. 7 is a third circuit embodiment illustrating a magnetic brush shortdetecting circuit adapted to shut down the reproduction machine in theevent shorting of a magnetic brush occurs.

For a general understanding of the illustrated copier/reproductionmachine in which the invention may be incorporated, reference is had toFIG. 1 in which the various system components for the machine areschematically illustrated.

A document 11 to be copied is placed upon a transparent support platenl6 fixedly arranged in an illumination assembly, generally indicated bythe reference numeral 10, positioned at the left end of the machine.Light rays from an illumination system are flashed upon the document toproduce image rays corresponding to the informational areas. The imagerays are projected by means of an optical system onto the photosensitivesurface of a xerographic plate in the form of a flexible photoconductivebelt 12 arranged on a belt assembly, generally indicated by thereference numeral 14.

The belt 12 comprises a photoconductive layer of selenium which is thelight receiving surface and imaging medium for the apparatus, on aconductive backing. The surface of the photoconductive belt is madephotosensitive by a previous step of uniformly charging the same bymeans of a corona generating device or corotron 13. Power for corotron13 is provided by a suitable power source.

The belt is journaled for continuous movement upon three rollers 20, 21and 22 positioned with their axes in parallel. The photoconductive beltassembly 14 is slidably mounted upon two support shafts 23 and 24, withthe roller 22 rotatably supported on the shaft 23 which is secured tothe frame of the apparatus and is rotatably driven by a suitable motorand drive assembly (not shown) in the direction of the arrow at aconstant rate. During exposure of the belt 12, the reflected light imageof such original document positioned on the platen is flashed on thesurface of the belt to produce an electrostatic latent image thereon atexposure station 27.

As the belt surface continues its movement, the electrostatic imagepasses through a developing station 28 in which there is positioned amagnetic brush developing apparatus, generally indicated by thereference numeral 30, and which provides development of theelectrostatic image by means of multiple brushes as the same movesthrough the development zone, as more fully hereinafter described.

The developed electrostatic image is transported by the belt to atransfer station 29 whereat a sheet of copy paper or transfer member ismoved between a transfer roller and the belt at a speed in synchronismwith the moving belt in order to accomplish transfer of the devlopedimage solely by an electrical bias on the transfer roller. There isprovided at this station a sheet transport mechanism, generallyindicated at 17, adapted to transport sheets of paper from a paperhandling mechanism, generally indicated by the reference numeral 18, tothe developed image on the belt at the station 29.

. After the sheet is stripped from belt 12, it is conveyed into a fuserassembly, generally indicated by the refer ence numeral 19, wherein thedeveloped and transferred xerographic powder image on the sheet materialis permanently affixed thereto. After fusing, the finished copy isdischarged from the apparatus at a suitable point for collectionexternally of the apparatus. The toner particles remaining as residue onthe developed image, background particles and those particles otherwisenot transferred are carried by the belt 12 to a cleaning apparatus 26positioned on the rim of the belt between rollers and 22 adjacent apre-clean corona generator 25. Further details regarding the structureof the belt assembly 14 and its relationship with the machine andsupport therefor may be found in the copending Application Serial No.102,312, assigned to the same assignee.

Referring to FIGS. 2 through 4, there is illustrated a magnetic brushdeveloping assembly, generally indicated as 30, comprising a series ofrollers 36 rotatably supported in frame end plates 32, 34. The rollers36 are comprised of a cylindrical sleeve 46 of a roughened surfaceformed of a non-permeable material and extending almost the length ofthe housing of the developing apparatus 30. End sleeves 48, formed of aninsulating material, are shrunk fit on each cylindrical sleeve 46adjacent the ends thereof. One end of the sleeve 46 is closed by a cap50 which supports a roller drive shaft 52 in coaxial alignment with thesleeve 46. The other end of the sleeve 46 is closed by a cap 54 havingan orifice 56 through which extends shaft 58 of the internal bar magnets61. Suitable bearing means 60 are provided to permit the sleeve 46 torotate relative to shaft 58.

The roller drive shafts 52 are suitably mounted in bearings in end plate32 and carry on their projecting ends drive sprockets 96. Sprockets 96are formed of an insulating material.

Referring specifically to FIGS. 2 and 3, the magnet roller assembly 30is disposed within a housing, generally indicated as 66, having agenerally rectangular cross section and a length extending beyond thewidth of the photoconductive belt 12. Housing 66 is substantially closedexcept for an opening opposite photoconductive belt 12 whereatdevelopment of the latent image on belt 12 is effected. Housing 66 ineffect serves as a container for developing material comprising carrierbeads from magnetizable material and colored electrostatic tonerparticles which adhere thereto.

To provide bias potential to rollers 36, a suitable wiper 70 is providedin electrical contact with magnet shafts 58, wiper 70 extending alongand being supported by side plate 34 to form an electrical path from asuitable power supply, shown schematically by battery 103, to each ofthe rollers 36. As will appear, in the FIG. 5 circuit embodiment thebrush short detecting circuit is in series with the voltage line 71while in the FIG. 6 circuit embodiment brush short detecting circuitsare provided in the biasing circuits to individual magnetic brushrollers.

During development, the rollers 36 are rotated in unison in the samedirection from a suitable drive source via sprockets 96, the internalbar magnets 61 remaining stationary. The brush bristles produced by theinfluence of the magnetic field emanating from the bar magnets 61 actingupon the magnetizable carrier beads in the developing material will formon the upper region of the sleeve 46 between the rollers 36 and thesurface of the selenium belt 12.

This takes the form of a magnetic blanket" extending continuously overall of the brushes of rollers 36 for the entire width of the developmentzone 28 wherein the material is disposed or available to some degree fordeveloping purposes. Further details regarding the formation and effectof the magnetic blanket" are described in the copending application Ser.No. 330,285, assigned to the same assignee.

Rollers 36 are biased to a predetermined voltage by battery 103, itbeing understood that the bias applied to magnetic brush rollers 36cooperates with the electrostatic charge on belt 12 to establish anelectrostatic development field in the developing area 28. The aforesaidelectrostatic development field serves to attract toner particles tophotoconductor belt 12 in conformance with the latent electrostaticimage on belt 12. As will be understood by those skilled in the art, theaforesaid electrostatic development field is essential if the latentimages on belt 12 are to be developed, and must be exactly controlled ifoptimum development of the latent image on belt 12 is to be attained.Accordingly, any uncontrolled change in the aforesaid electrostaticdevelopment field, such as occurs on shorting of one or more of themagnetic brush rollers 36, may degrade the image developed to a pointwhere it is less than satisfactory.

The developing material normally comprises a carrier, usually smallmetal beads, and toner or ink particles. The carrier beads and toner arechosen for their triboelectric relationship.

The metal carrier beads may bear a coating of a suitable releasematerial, and this type of bead, so long as the coating is perfect andremains intact and not worn off, is insulated. Other developingmaterials use uncoated metal beads. Should carrier beads of this typejam or compress together between a magnetic brush roller 36 and thehousing 66, a current or ground path is formed, shorting the brush andchanging the brush magnetic force. In addition, metal contaminants maybe present in the developing material and this may short out one or moreof the magnetic brush rollers 36.

Referring particularly to the circuit of FIG. 5, line 71 series connectsmagnetic brush rollers 36 with one another and with battery 103. Asuitable indicator, which may comprise neon type lamp 110, is disposedin series with line 71. A suitable resistor 111 is provided in parallelwith lamp 110. In this embodiment, a ground short in one or more of themagnetic brush rollers 36 increases the current flow through resistor11] thereby generating sufficient voltage to cause lamp 110 to light.Preferably, lamp 110 is placed where it can be conveniently observed bythe operator.

In the circuit embodiment of FIG. 6, a lamp 110' is series connected inthe biasing circuit to each of the individual magnetic brush rollers 36.A resistor 111' parallels each lamp 110'.

On a short in one of the brush rollers 36, the lamp 110' associatedtherewith lights. By this arrangement, the operator is able tospecifically identify the particular magnetic brush roller 36 shorted.Preferably, lamps 110 are disposed where they may be conveniently seenby the operator.

Instead of visually identifying or signalling the presence of a short inone of the magnetic brush rollers 36, or as an adjunct thereto, directcontrol may be exercised over operation of copier 10. In the schematiccircuit representation of FIG. 7 a normally closed control switch 115 isprovided in the control circuit 116 of copier 10. A suitable currentsensitive switch relay 117 is arranged in series relationship with thebias line 71 to the magnetic brush rollers 36.

In the event of a short in any one of the magnetic brush rollers 36, thechange in current through relay 117 energizes relay 117 to open switch115 and actuate copier shutdown circuit 116. Circuit 116 stops copierl0, normally through a cycle out process. For this purpose suitablelock-out means (not shown) may be provided to inhibit restarting ofcopier 10 until the short condition has been corrected.

Other circuit arrangements for effectuating shutdown of the copier inthe event of a short in one or more of the magnetic brush rollers 36 maybe contemplated.

While the invention has been described with reference to the structuredisclosed, it is not confined to the details set forth, but is intendedto cover such modifications or changes as may come within the scope ofthe following claims.

What is claimed is:

1. In a reproduction machine for producing copies of originals having aphotoconductive member on which latent electrostatic images of theoriginal being reproduced are formed, with means for developing saidlatent electrostatic images in preparation for transfer thereof tosupport material, said developing means including at least one magneticbrush, together with biasing means to provide a biasing voltage on saidmagnetic brush, the improvement comprising:

signal indicator means;

energizing means for energizing said signal indicator means to produce asignal; and

brush short responsive means responsive to shorting of said magneticbrush to actuate said energizing means whereby to produce said signal.

2. The reproduction machine according to claim 1 in which said signalindicator means comprises a light.

3. The reproduction machine according to claim 1 in which said signalindicator means comprises means to shut down said reproduction machineon shorting of said magnetic brush.

4. The reproduction machine according to claim 1 in which saiddeveloping means includes at least two magnetic brushes, said signalindicator means comprising an indicator element for each of saidbrushes, said short responsive means responding to a short in one ofsaid brushes to actuate said energizing means to energize the indicatorelement associated with said one brush.

5. As a control for visually indicating the presence of a short circuitin the magnetic brush developer section of an electrostatic typereproduction machine, said developer section having at least onemagnetic develop ing brush, together with circuit means for imposing anoperating bias on said brush, the combination comprising:

signal means in said circuit means in series relationship with saidmagnetic brush; and

means responsive to a predetermined change in current in said circuitmeans to actuate said signal means.

6. The control according to claim 5 in which said developer sectionincludes plural magnetic brushes, said circuit means providing anindividual bias circuit to each of said magnetic brushes, and

signal means in each of said magnetic brush circuits.

7. In a magnetic brush developing apparatus for reproduction machines,said developing apparatus including a housing within which developingmaterial including bead-like particles of metallic carrier is provided,together with at least one roll-type magnetic brush disposed inoperative relationship with said developing material, said magneticbrush being biased whereby to magnetically generate on the surfacethereof a blanket-like covering of said developing material for use indeveloping latent electrostatic images, the combination of:

signal producing means;

energizing means for energizing said signal producing means to produce asignal; and

means responsive to grounding of said magnetic brush through saiddeveloping material carrier to actuate said energizing means wherebysaid signal producing means is energized and a signal reflectinggrounding of said brush is produced.

1. In a reproduction machine for producing copies of originals having aphotoconductive member on which latent electrostatic images of theoriginal being reproduced are formed, with means for developing saidlatent electrostatic images in preparation for transfer thereof tosupport material, said developing means including at least one magneticbrush, together with biasing means to provide a biasing voltage on saidmagnetic brush, the improvement comprising: signal indicator means;energizing means for energizing said signal indicator means to produce asignal; and brush short responsive means responsive to shorting of saidmagnetic brush to actuate said energizing means whereby to produce saidsignal.
 2. The reproduction machine according to claim 1 in which saidsignal indicator means comprises a light.
 3. The reproduction machineaccording to claim 1 in which said signal indicator means comprisesmeans to shut down said reproduction machine on shorting of saidmagnetic brush.
 4. The reproduction machine according to claim 1 inwhich said developing means includes at least two magnetic brushes, saidsignal indicator means comprising an indicator element for each of saidbrushes, said short responsive means responding to a short in one ofsaid brushes to actuate said energizing means to energize the indicatorelement associated with said one brush.
 5. As a control for visuallyindicating the presence of a short circuit in the magnetic brushdeveloper section of an electrostatic type reproduction machine, saiddeveloper section having at least one magnetic developing brush,together with circuit means for imposing an operating bias on saidbrush, the combination comprising: signal means in said circuit means inseries relationship with said magnetic brush; and means responsive to apredetermined change in current in said circuit means to actuate saidsignal means.
 6. The control according to claim 5 in which saiddeveloper section includes plural magnetic brushes, said circuit meansproviding an individual bias circuit to each of said magnetic brushes,and signal means in each of said magnetic brusH circuits.
 7. In amagnetic brush developing apparatus for reproduction machines, saiddeveloping apparatus including a housing within which developingmaterial including bead-like particles of metallic carrier is provided,together with at least one roll-type magnetic brush disposed inoperative relationship with said developing material, said magneticbrush being biased whereby to magnetically generate on the surfacethereof a blanket-like covering of said developing material for use indeveloping latent electrostatic images, the combination of: signalproducing means; energizing means for energizing said signal producingmeans to produce a signal; and means responsive to grounding of saidmagnetic brush through said developing material carrier to actuate saidenergizing means whereby said signal producing means is energized and asignal reflecting grounding of said brush is produced.